go/format, cmd/gofmt: avoid dependency on internal package format

Fixes #11844.

Change-Id: I32edd39e79f7c9bdc132c49bd06081f35dac245d
Reviewed-on: https://go-review.googlesource.com/15114
Reviewed-by: Alan Donovan <adonovan@google.com>

5 files changed, 186 insertions, 20 deletions

diff --git a/src/cmd/gofmt/gofmt.go b/src/cmd/gofmt/gofmt.go
index b2805ac05f..cfebeffe4a 100644
--- a/src/cmd/gofmt/gofmt.go
+++ b/src/cmd/gofmt/gofmt.go
@@ -13,7 +13,6 @@ import (
 	"go/printer"
 	"go/scanner"
 	"go/token"
-	"internal/format"
 	"io"
 	"io/ioutil"
 	"os"
@@ -88,7 +87,7 @@ func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error
 		return err
 	}
 
-	file, sourceAdj, indentAdj, err := format.Parse(fileSet, filename, src, stdin)
+	file, sourceAdj, indentAdj, err := parse(fileSet, filename, src, stdin)
 	if err != nil {
 		return err
 	}
@@ -107,7 +106,7 @@ func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error
 		simplify(file)
 	}
 
-	res, err := format.Format(fileSet, file, sourceAdj, indentAdj, src, printer.Config{Mode: printerMode, Tabwidth: tabWidth})
+	res, err := format(fileSet, file, sourceAdj, indentAdj, src, printer.Config{Mode: printerMode, Tabwidth: tabWidth})
 	if err != nil {
 		return err
 	}
diff --git a/src/cmd/gofmt/internal.go b/src/cmd/gofmt/internal.go
new file mode 100644
index 0000000000..fc7f976af9
--- /dev/null
+++ b/src/cmd/gofmt/internal.go
@@ -0,0 +1,166 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// TODO(gri): This file and the file src/go/format/internal.go are
+// the same (but for this comment and the package name). Do not modify
+// one without the other. Determine if we can factor out functionality
+// in a public API. See also #11844 for context.
+
+package main
+
+import (
+	"bytes"
+	"go/ast"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"strings"
+)
+
+// parse parses src, which was read from the named file,
+// as a Go source file, declaration, or statement list.
+func parse(fset *token.FileSet, filename string, src []byte, fragmentOk bool) (
+	file *ast.File,
+	sourceAdj func(src []byte, indent int) []byte,
+	indentAdj int,
+	err error,
+) {
+	// Try as whole source file.
+	file, err = parser.ParseFile(fset, filename, src, parserMode)
+	// If there's no error, return.  If the error is that the source file didn't begin with a
+	// package line and source fragments are ok, fall through to
+	// try as a source fragment.  Stop and return on any other error.
+	if err == nil || !fragmentOk || !strings.Contains(err.Error(), "expected 'package'") {
+		return
+	}
+
+	// If this is a declaration list, make it a source file
+	// by inserting a package clause.
+	// Insert using a ;, not a newline, so that the line numbers
+	// in psrc match the ones in src.
+	psrc := append([]byte("package p;"), src...)
+	file, err = parser.ParseFile(fset, filename, psrc, parserMode)
+	if err == nil {
+		sourceAdj = func(src []byte, indent int) []byte {
+			// Remove the package clause.
+			// Gofmt has turned the ; into a \n.
+			src = src[indent+len("package p\n"):]
+			return bytes.TrimSpace(src)
+		}
+		return
+	}
+	// If the error is that the source file didn't begin with a
+	// declaration, fall through to try as a statement list.
+	// Stop and return on any other error.
+	if !strings.Contains(err.Error(), "expected declaration") {
+		return
+	}
+
+	// If this is a statement list, make it a source file
+	// by inserting a package clause and turning the list
+	// into a function body.  This handles expressions too.
+	// Insert using a ;, not a newline, so that the line numbers
+	// in fsrc match the ones in src. Add an extra '\n' before the '}'
+	// to make sure comments are flushed before the '}'.
+	fsrc := append(append([]byte("package p; func _() {"), src...), '\n', '\n', '}')
+	file, err = parser.ParseFile(fset, filename, fsrc, parserMode)
+	if err == nil {
+		sourceAdj = func(src []byte, indent int) []byte {
+			// Cap adjusted indent to zero.
+			if indent < 0 {
+				indent = 0
+			}
+			// Remove the wrapping.
+			// Gofmt has turned the ; into a \n\n.
+			// There will be two non-blank lines with indent, hence 2*indent.
+			src = src[2*indent+len("package p\n\nfunc _() {"):]
+			// Remove only the "}\n" suffix: remaining whitespaces will be trimmed anyway
+			src = src[:len(src)-len("}\n")]
+			return bytes.TrimSpace(src)
+		}
+		// Gofmt has also indented the function body one level.
+		// Adjust that with indentAdj.
+		indentAdj = -1
+	}
+
+	// Succeeded, or out of options.
+	return
+}
+
+// format formats the given package file originally obtained from src
+// and adjusts the result based on the original source via sourceAdj
+// and indentAdj.
+func format(
+	fset *token.FileSet,
+	file *ast.File,
+	sourceAdj func(src []byte, indent int) []byte,
+	indentAdj int,
+	src []byte,
+	cfg printer.Config,
+) ([]byte, error) {
+	if sourceAdj == nil {
+		// Complete source file.
+		var buf bytes.Buffer
+		err := cfg.Fprint(&buf, fset, file)
+		if err != nil {
+			return nil, err
+		}
+		return buf.Bytes(), nil
+	}
+
+	// Partial source file.
+	// Determine and prepend leading space.
+	i, j := 0, 0
+	for j < len(src) && isSpace(src[j]) {
+		if src[j] == '\n' {
+			i = j + 1 // byte offset of last line in leading space
+		}
+		j++
+	}
+	var res []byte
+	res = append(res, src[:i]...)
+
+	// Determine and prepend indentation of first code line.
+	// Spaces are ignored unless there are no tabs,
+	// in which case spaces count as one tab.
+	indent := 0
+	hasSpace := false
+	for _, b := range src[i:j] {
+		switch b {
+		case ' ':
+			hasSpace = true
+		case '\t':
+			indent++
+		}
+	}
+	if indent == 0 && hasSpace {
+		indent = 1
+	}
+	for i := 0; i < indent; i++ {
+		res = append(res, '\t')
+	}
+
+	// Format the source.
+	// Write it without any leading and trailing space.
+	cfg.Indent = indent + indentAdj
+	var buf bytes.Buffer
+	err := cfg.Fprint(&buf, fset, file)
+	if err != nil {
+		return nil, err
+	}
+	res = append(res, sourceAdj(buf.Bytes(), cfg.Indent)...)
+
+	// Determine and append trailing space.
+	i = len(src)
+	for i > 0 && isSpace(src[i-1]) {
+		i--
+	}
+	return append(res, src[i:]...), nil
+}
+
+// isSpace reports whether the byte is a space character.
+// isSpace defines a space as being among the following bytes: ' ', '\t', '\n' and '\r'.
+func isSpace(b byte) bool {
+	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
+}
diff --git a/src/cmd/gofmt/long_test.go b/src/cmd/gofmt/long_test.go
index df9a878df4..237b86021b 100644
--- a/src/cmd/gofmt/long_test.go
+++ b/src/cmd/gofmt/long_test.go
@@ -15,7 +15,6 @@ import (
 	"go/ast"
 	"go/printer"
 	"go/token"
-	"internal/format"
 	"io"
 	"os"
 	"path/filepath"
@@ -33,7 +32,7 @@ var (
 )
 
 func gofmt(fset *token.FileSet, filename string, src *bytes.Buffer) error {
-	f, _, _, err := format.Parse(fset, filename, src.Bytes(), false)
+	f, _, _, err := parse(fset, filename, src.Bytes(), false)
 	if err != nil {
 		return err
 	}
@@ -61,7 +60,7 @@ func testFile(t *testing.T, b1, b2 *bytes.Buffer, filename string) {
 
 	// exclude files w/ syntax errors (typically test cases)
 	fset := token.NewFileSet()
-	if _, _, _, err = format.Parse(fset, filename, b1.Bytes(), false); err != nil {
+	if _, _, _, err = parse(fset, filename, b1.Bytes(), false); err != nil {
 		if *verbose {
 			fmt.Fprintf(os.Stderr, "ignoring %s\n", err)
 		}
diff --git a/src/go/format/format.go b/src/go/format/format.go
index 1adfd7d45e..b9cacfebd8 100644
--- a/src/go/format/format.go
+++ b/src/go/format/format.go
@@ -12,7 +12,6 @@ import (
 	"go/parser"
 	"go/printer"
 	"go/token"
-	"internal/format"
 	"io"
 )
 
@@ -82,7 +81,7 @@ func Node(dst io.Writer, fset *token.FileSet, node interface{}) error {
 //
 func Source(src []byte) ([]byte, error) {
 	fset := token.NewFileSet()
-	file, sourceAdj, indentAdj, err := format.Parse(fset, "", src, true)
+	file, sourceAdj, indentAdj, err := parse(fset, "", src, true)
 	if err != nil {
 		return nil, err
 	}
@@ -93,7 +92,7 @@ func Source(src []byte) ([]byte, error) {
 		ast.SortImports(fset, file)
 	}
 
-	return format.Format(fset, file, sourceAdj, indentAdj, src, config)
+	return format(fset, file, sourceAdj, indentAdj, src, config)
 }
 
 func hasUnsortedImports(file *ast.File) bool {
diff --git a/src/internal/format/format.go b/src/go/format/internal.go
index a8270ba669..2850a43068 100644
--- a/src/internal/format/format.go
+++ b/src/go/format/internal.go
@@ -2,6 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// TODO(gri): This file and the file src/cmd/gofmt/internal.go are
+// the same (but for this comment and the package name). Do not modify
+// one without the other. Determine if we can factor out functionality
+// in a public API. See also #11844 for context.
+
 package format
 
 import (
@@ -13,11 +18,9 @@ import (
 	"strings"
 )
 
-const parserMode = parser.ParseComments
-
-// Parse parses src, which was read from the named file,
+// parse parses src, which was read from the named file,
 // as a Go source file, declaration, or statement list.
-func Parse(fset *token.FileSet, filename string, src []byte, fragmentOk bool) (
+func parse(fset *token.FileSet, filename string, src []byte, fragmentOk bool) (
 	file *ast.File,
 	sourceAdj func(src []byte, indent int) []byte,
 	indentAdj int,
@@ -85,10 +88,10 @@ func Parse(fset *token.FileSet, filename string, src []byte, fragmentOk bool) (
 	return
 }
 
-// Format formats the given package file originally obtained from src
+// format formats the given package file originally obtained from src
 // and adjusts the result based on the original source via sourceAdj
 // and indentAdj.
-func Format(
+func format(
 	fset *token.FileSet,
 	file *ast.File,
 	sourceAdj func(src []byte, indent int) []byte,
@@ -109,7 +112,7 @@ func Format(
 	// Partial source file.
 	// Determine and prepend leading space.
 	i, j := 0, 0
-	for j < len(src) && IsSpace(src[j]) {
+	for j < len(src) && isSpace(src[j]) {
 		if src[j] == '\n' {
 			i = j + 1 // byte offset of last line in leading space
 		}
@@ -150,14 +153,14 @@ func Format(
 
 	// Determine and append trailing space.
 	i = len(src)
-	for i > 0 && IsSpace(src[i-1]) {
+	for i > 0 && isSpace(src[i-1]) {
 		i--
 	}
 	return append(res, src[i:]...), nil
 }
 
-// IsSpace reports whether the byte is a space character.
-// IsSpace defines a space as being among the following bytes: ' ', '\t', '\n' and '\r'.
-func IsSpace(b byte) bool {
+// isSpace reports whether the byte is a space character.
+// isSpace defines a space as being among the following bytes: ' ', '\t', '\n' and '\r'.
+func isSpace(b byte) bool {
 	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
 }